When The Earth Was Purple

Why does chlorophyll appear green to us?

• It absorbs blue and red light and reflects green light.

• It reflects all colors except green.

• It absorbs all colors equally.

• It absorbs green light and reflects blue and red light.

What is the Purple Earth hypothesis?

• The belief that Earth will turn purple in the future.

• The theory that early photosynthesizers used a purple pigment instead of chlorophyll.

• The idea that Earth was once covered in purple oceans.

• The hypothesis that purple light is more efficient for photosynthesis.

What pigment do halo bacteria use to absorb light?

• Chlorophyll

• Carotene

• Retinal

• Xanthophyll

What event is known as the Great Oxygenation Event?

• The period when Earth first formed an atmosphere.

• The era when plants first appeared on land.

• The time when oxygen levels in Earth's atmosphere drastically increased.

• The extinction of dinosaurs due to oxygen depletion.

How did some halo bacteria survive the increase in oxygen levels?

• By moving to oxygen-free environments.

• By evolving to produce oxygen themselves.

• By developing a resistance to oxygen.

• By acquiring genes from other microbes.

What could the Purple Earth hypothesis imply for the search for life on other planets?

• All extraterrestrial life will be purple.

• Planets with no light absorption are lifeless.

• Life on other planets might not use chlorophyll.

• We should only look for planets with green vegetation.

Why might it be important to search for planets that reflect less red light?

• It shows the planet has a thick atmosphere.

• It means the planet is closer to its star.

• It suggests the presence of chlorophyll-using organisms.

• It indicates the presence of water.